Recovery of naphthalene



Dec. 20, 1955 R. H. BROWN ETAL RECOVERY OF NliPi-ITI-IJE'NE4 Filed March 20, 1953 MQvmSl/Il/ ATTORNEY MM .w

United States Patent'4 RECOVERY oF NAPHTHALENE Russell H. Brown and Walter D. Schmidt, Hammond, Ind., assignors to Standard Oil Company, Chicago, iii., .a corporation of Indiana Application lVIarch 20, 1953, Serial No. 343,762

5 Claims. (Cl. 196-50) Naphthalene is present in many crude oils, particularly the highly aromatic Mexican, California and West Texas crudes. Also, naphthalene is present in oils derived from the refining of petroleum hydrocarbons. Substantial quantities of naphthalene are present in the heavy naphtha from thermal cracking and catalytic cracking of gas oils.

The various conversion processes utilizing a catalyst in the presence of hydrogen such as platforming, catforming and hydroforming produce naphthalene in appreciable quantities. The aromatic and naphthene concentrates obtained by the solvent rening of naphthas and light gas oils also contain naphthalene in appreciable amounts.

However, it is impractical to attempt the recovery of this naphthalene because the alkylberlenes and naphthenes which boil at about the same temperature as naphthalene interfere with its recovery either by superfrac tionation orby crystallization. Naphthalene has been produced from these cuts by destructive hydrogenation followed by multiple fractional crystallization.

An object of this invention is the recovery of naphthalene from a close-boiling mixture of naphthalene, alkylf benzenes and/or naphthenes, from which mixture the naphthalene cannot be recovered by fractional crystallization'. Another object is the recovery of .naphthalene by fractional distillation of the product from the catalytic cracking of a mixture of hydrocarbons containing naphthaleue which boils at about the boiling point of naphthalene. A particular object is the recovery of naphthalene from a solventi extract of a cracked gas oil. Still another particular object is a combination process for the solvent extraction of a catalytically cracked gas oil, the I separation of a naphthalene boiling range fraction; the catalytic cracking of 'said fraction and the recovery of substantially pure naphthalene from the product-of said cat cracking by fractional distillation. Other objects will become apparent in the course of the detailed description of this invention.

It has been discovered that a substantially pure naphthalene can be recovered from a mixture of naphthalene, alkylbenzenes and/or naphthenes, by the catalytic cracking of said mixture and a subsequent fractional distillation of the liquid product from the catalytic cracking operation.

More particularly it has been found that good yields of naphthalene can be obtained from a catalytically cracked gas oil by (l) solvent extracting said gas oil to recover an aromatic-naphthene-rich extract, (2) fractionally distilling'said extract to obtain a fraction boiling between about`385" and 455"v F., (3) catalytically cracking said fraction, and (4) fractionally distilling the liquid product froin' said catalytic cracking to recover a substantially pure naphthalene product. i

.The invention is described in detail in conjunction with the description of the annexed drawing, which drawing 2,721,854 Patented Dec.; 20, 1955 ICC forms a part of this specication. It is to be understood that this drawing is schematic in nature and does not in clude many items of process equipment, which items may be readily added thereto by one skilled in the art. It is not intended that this specific illustration shall limit the scope of this invention.

The feed to the process may be obtained by superfractional distillation of a petroleum hydrocarbon mixture which contains napthalene. Or, more practically, by the fractional distillation of a hydrocarbon mixture such as hydroformate or platformate, or preferably by the fractional distillation of a solvent extract obtained from a petroleum hydrocarbon mixture containing appreciable amounts of naphthalene. in this illustration the feed consists of a catalytically cracked gas oil; the charge to the catalytic cracking operation consisted of a mixture of gas oils obtained from the distillation of West Texas and Mid-Continent crude.

Feed from source 11 is passed through line 12 into deaerator 13. Deaerator 1?- is a conventional system for removing dissolved air from the feed. The deaerated feed is passed through line 14 into drier 16. Drier 16 may be any conventional method for removing dissolved water from the feed. Herein a vessel filled with alumina spheres is used. .lf desired the feed may be deaerated and dried in a single step by a partial ilashing operation in which a small amount of the lowest boiling hydrocarbons ar'e distilled along with the dissolved air and water.

The deaerated and dried feed is passed through line 17, heat exchanger 18 and line 19 into extractor 21. Extractor 21 is a vertical vessel provided with means for adequately contacting the charge and a selective solvent. Vessel 21 may contain packing such as Raschig rings, Berl saddles, ceramic balls, etc., or it may be provided with perforated plates or bubble trays. Extractor 21 is provided with heat exchange coils 22, 23 and 24. These coils maintain the temperature in the extractor at the desired point or may be used to provide a temperature gradient over the height of the extractor.

The selective solvent used may be any one of the well known solvents used in petroleum refining such as liquid SO2, nitrobenzene, furfural, benzol, ,8,'dichloroethyl ether, etc. in this illustration liquid SO2 is used. The liquid SO2 from source 26 is passed by way of line 27 into the upper portion of extractor 21. it is to be understood that the liquid SO2 may be introduced at several points along the height of the extractor. tration 150 volume percent of liquid SO2 is used, based on the charge introduced into extractor 21 by Way of line 19,-and the extractor is operated at a uniform temperature of -l0 C. 1-14 E). The extractorV is operated with a high level phase boundary, i. e., the extract just below'the point of entry of phase extends to Ja point the liquid SO2. v

The raffinate phase is withdrawn from a point near the top of the extractor 21 and is passed by way of line 31, heat exchanger 32 and line 33 into stripper 34. Stripper 34 is provided with an internal heat exchanger 36 and with some fractionation trays not shown. The SO2 dissolved and occluded in the raflnate phase is distilled overhead and is withdrawn from stripper 34 by way of lines 37 and 3S. The raflinate is Withdrawn from the bottom of stripper 34 by way of line 39 and is sent to storage not shown.

This raffinate is low in aromatic hydrocarbons and is quite substantially reduced in sulfur content. This raffinate may be used as a good quality heater oil or it may be recycled to the catalytic cracking of mixed gas oil.

The extract phase is withdrawn from extractor 21 and is passed by way of vline 41, heat exchanger 42 and line 43 into stripper 44. Stripper 44 is provided with an internal heat exchanger 46 andv fractionation trays not In this illus-v 3 shown. In stripper 44 the SO2 is distilled overhead and is withdrawn by way of lines 47 and 48.

The `SO2 distilled from strippers 34 and 44 is passed by way of a common line 49.to a purification zone 51. In purification zone 51 the SO2 is freed of impurities such as HnS which are picked up from the extraction and stripping operations. Purification zone 51 may be any form such as is conventionally used in commercial liquid SO2 extraction operations. The purified SO2 is passed by way of line 52, heat exchanger 53 and line 54 to line 27 for reuse in the solvent extraction step.

The extract from stripper 44 is passed by way of line 61, heat exchanger 62 and line 63 into fractionator 64. Fractionator 64 is provided with internal heat exchanger 66 and fractionation trays not shown. Fractionator 64 represents schematically the distillative separation of the extract into a fraction boiling below about 385 F., an intermediate fraction boiling between about 385 and 455 F. and a fraction boiling above 455 F. The lowest boiling fraction is taken overhead by way of line 68. This fraction, after a suitable desulfurization operation, may be added to aviation gasoline as a high octane number component. The highest boiling fraction is withdrawn from fractionator 64 as a liquid bottoms product by way of line 69. This fraction may be utilized as a source of high solvency naphthas or may be cycled to the catalytic cracking of mixed gas oil.

The intermediate fraction is withdrawn from fractionator 64 .and is passed by way of line 71 into fractionator 72.. Fractionator 72 is provided with internal heater 73 and fractionation trays not shown. In fractionator 72 the intermediate fraction is split into a low boiling fraction boiling below about 400 F., an intermediate fraction boiling between about 400 and 440 F. and a high boiling fraction boiling above 440 F. The low boiling fraction is taken overhead by way of line 76 and passed to storage not shown; or this fraction may be passed by way of valved line 77 to line 68 and mixed with the lower boiling fraction from fractionator 64. The highest boiling fraction is withdrawn from the bottom of fractionator 72 by way of line 78 and sent to storage not shown; or it may be passed by way of valved line 79 to line 69 and mixed with the highest boiling fraction from fractionator 64.

It is to be understood that the 385 to 455 F. fraction from fractionator 64 may be utilized as such in this process. However, in order to essentially eliminate the presence of methyl naphthalene from the naphthalene fraction it is preferred to operate with a fraction boiling substantially below the boiling point of methyl naphthar lene, which boiling point is about 465 F., i. e., the preferred boiling range of the naphthalene fraction from a solvent extract is between about 400 and 440 F. It is possible to produce an essentially pure naphthalene by the process of this invention by using a fraction boiling closely about the boiling point of naphthalene, i. e., about 424.2" F.

The naphthalene fraction boiling between about 400 and 440 F. is withdrawn from fractionator 72 and is passed by way of line 81 to furnace 82. Furnace 82 is a conventional type of relinery heater. In furnace 82 the temperature of the naphthalene fraction is raised to about 950 F. at a pressure suciently low to permit all of said fraction to be vaporized. The vapors are passed from furnace 82 by way of line 83 into catalytic reactor 84.

Catalytic reactor 84 is a reaction vessel provided with a ixed bed of silica-alumina catalyst. The vapors crack in the presence of the catalyst to produce a liquid product and coke, which coke is deposited on the catalyst. The vapors of the liquid product are passed by way of line 86, heat exchanger 87 and line 88 into fractionator 89, which is provided with internal heat exchanger 91.

.It is to be understood that this fixed bed catalytic reaction is schematic in nature. The operation shown here represents the conventional tixed bed Houdry catalytic Y 4 l cracking operation. All of the catalysts conventionally used for the catalytic cracking of petroleum hydrocarbons, in the absence of added hydrogen, may be used in the catalytic cracking operation of this invention.

Although a xed bed operation is shown herein, other types of catalytic cracking may be utilized, e. g., the Well known fluid catalytic cracking process which utilizes a iluid bed; and the Thermofor catalytic cracking and Houdry flow catalytic cracking processes which utilize moving beds. y

The temperature of operation may be that convention ally used in these catalytic cracking processes such as between about 800 and 1l00 F.

From fractionator 89 an overhead stream of materials boiling in the gasoline range are withdrawn by way of line 93. A bottoms product boiling above about 435 F. is withdrawn from fractionator 89 by way of line 94. An intermediate fraction is withdrawn and is passed vby way of line 96 into fractionator 97. Fractionator 97 is provided with an internal heat exchanger 98.

In fractionator 97 a fraction boiling in the naphthalene boiling range, i. e., 424i1 F. is withdrawn by Way of line 101. A lower boiling fraction is withdrawn overhead by way of line 102 and may be passed vby way of line 103 to line 93. These lower boiling fractions are of very high octane number and are excellent components for aviation gasoline. The higher boiling fraction is withdrawn from fractionator 97 by way of line 106 and may be passed by way of line 107 to line 94. These higher boiling fractions are excellent high solvency naphthas.

The naphthalene product of this process contains an appreciable amount of sulfur and very slight amounts of non-naphthalene hydrocarbons. The sulfur may readily be removed by sulfuric acid treating. An essentially pure naphthalene product can be obtained by fractional crystal. lization of the desulfurized material.

It is to be understood that a naphthalene fraction consisting of naphthalene, alkylbenzenes and/or naphthenes may be derived from petroleum refining operations by methods other than solvent extraction. 'Ihe naphthalene in this naphthalene fraction can be recovered by catalytically cracking this fraction without the prior solvent extraction and fractionation steps shown in the drawing, i. e., this particular feed may be introduced directly into furnace 82.

By way of illustration of the results obtainable with this process, the following is set out: Y

A light catalytic cycle oil was obtained by the distillation of the liquid product from the fluid catalytic cracking of a West Texas virgin gas oil, using silica-alumina cata- This feed oil was extracted with liquid sulfur dioxide. The extraction was carried out in three batch stages, `using 27 volume percent of liquid SO2, based on oil charged to each stage; the temperature in each stage was 20 C. (-4 R). This method of extraction corresponds approximately to a three-stage continuous countercurrent operation, using about 40 volume percent oiv liquid SO2, based on charge oil. The ultimate yields in this three` stage batch operation were: raffinate, 51.5 volume per" cent; extract, 48.5 volume percent. The sulfur contents were raiiinate, 0.18 weight percent and extract, 1.97e

weight percent.

The total extract phase was subjected to distillation in an Oldershaw column. Five cuts were obtained as follows:

Cuts 1, 2 and 3 were combined into a naphthalene fraction. No separation of naphthalene crystals was obtained even though this naphthalene fraction was cooled at C. (32 F.). The melting point of pure naphthalene is +80.2 C. (+176.4 R).

In an attempt to produce naphthalene by crystallization from a distillate, 200 m1. of the total extract were separated into twenty cuts by means of a Hyper Cal column. The Hyper Cal column was operated at 760 mm. at a throughput rate of 300 ml. per hour, a reflux ratio of 50 to l, and a product rate of 6 ml. per hour. Each cut was cooled to -1-20 C. ({-6S F.) without obtaining any separation of naphthalene crystals.

A fixed bed unit was used for the catalytic cracking of the extract. This unit was charged with synthetic silicaalumina microspheres (National Aluminate Company). The fresh catalyst was conditioned with steam at 1000n F. for 1 hour and with dry air for 3 hours. The cracking was carried out at a temperature of 930 F. at 15 p. s. i. a. and a reciprocal space velocity, weight of catalyst per weight of oil per hour, of 0.227. The total run time was 60 minutes.

Two catalytic cracking runs were carried out. In one run the feed was the naphthalene fraction produced by Oldershaw distillation. In this run the amount of coke deposited on the catalyst was 1.25 weight percent, based on feed oil. The total liquid product obtained by catalytic cracking of the naphthalene fraction was distilled using a three-plate Hempel column. A yield, based on total liquid product, of 5 0 volume percent of naphtha boiling below 410 F. was obtained. This naphtha had a sulfur content of 0.3 weight percent and had an aromatic content of 90 volume percent (sulfonation method). The Blending octane number of this naphtha was obtained by the CFR-R method in a 50-50 blend with regular gasoline base plus 1.5 cc. of tetraethyl lead per gallon; the Blending octane number of the naphtha was 98.7.

The bottoms fraction from the Hempel distillation was transferred to a Hyper Cal and distilled. The fraction boiling at 760 mm. between 215.8 C. and 22l.8 C. (420.4 and 431.2 F.) was chilled at 22 C. (+72 F.). The solid material was iiltered from the liquid material. This solid material contained 0.10 weight percent sulfur and analyzed 98.4 weight percent naphthalene (ultraviolet technique). The yield of naphthalene product based on naphthalene fraction was 12 volume percent. 'The above naphthalene product can be further puriiied into an essentially pure naphthalene by recrystallization and by sulfuric acid treatment to remove sulfur. Instead of this particular high purity naphthalene product a product equivalent to ordinary commercial grade naphthalene can be obtained by substituting a simpler fractionation technique for the superfractionation technique actually employed.

CII

Cal

A portion of the total extract was catalytically cracked in the manner described above. The total liquid product was fractionated in a manner similar to that described above to obtain a fraction boiling from 215.8 to 221.8" C. No solid naphthalene product could be obtained by cooling this cut to +22 C.

The above data clearly show that the process of this invention permits the recovery of high purity naphthalene from a naphthalene containing petroleum hydrocarbon.

It is believed that the interfering alkylbenzenes and naphthenes are converted to products that boil below and above naphthalene and thereby permit the recovery of substantially pure naphthalene by superfractional distillation of the liquid product from the catalytic cracking operation.

Thus having described the invention, what is claimed 1s:

l. A process for the recovery of naphthalene, which process comprises (1) treating a petroleum fraction containing naphthalene, alkylbenzenes and naphthenes boiling at about the boiling point of naphthalene With a selective solvent for aromatic and naphthene hydrocarbons, separating a raflnate phase from an extract phase containing said hydrocarbons and recovering said hydrocarbons from said extract phase, (2) distillatively separating a naphthalene fraction boiling within the range of between about 385 and 455 F. from said extract hydrocarbons, (3) subjecting said naphthalene fraction to a catalytic cracking operation, and (4) distillatively separating from the liquid product of said cracking a naphthalene product fraction.

2. The process of claim 1 wherein the fraction of step (4) is subjected to a crystallization operation in order to recover a high purity naphthalene product.

3. The process of claim 1 wherein the naphthalene fraction of step (2) boils between about 400 and 440 F.

4. A process for the recovery of naphthalene, which process comprises (A) extracting a catalytically cracked gas oil with liquid sulfur dioxide to obtain a naphthalenecontaining extract hydrocarbon mixture, (B) distilling said extract to obtain a naphthalene-containing fraction boiling within the range of about 385 to 455 F., (C) catalytically cracking said fraction at a temperature between about 800 and 1100 F., (D) distilling the liquid product from said cracking to obtain a cut boiling closely about the boiling point of naphthalene and (E) crystallizing a high purity naphthalene product from the cut of step (D).

5. The process of claim 4 wherein said cracking is carried out at about 900 F. in the presence of a silica-alumina catalyst.

References Cited in the iile of this patent UNITED STATES PATENTS 2,194,449 Sachanen et al. Mar. 19, 1940 2,304,289 Tongberg Dec. 8, 1942 2,374,387 Shipp et al. Apr. 24, 1945 2,436,257 Hansford et al. Feb. 17, 1948 2,526,881 Kunreuther et al. Oct. 24, 1950 2,642,465 Haddad et al. June 16, 1953 OTHER REFERENCES Benzol, S. E. Whitehead, D. Van Nostrand Co., New York (1920), pages 113 to 117. 

1. A PROCESS FOR THE RECOVERY OF NAPHTHALENE, WHICH PROCESS COMPRISES (1) TREATING A PETROLEUM FRACTION CONTAINING NAHTHALENE, ALKYLBENZENES AND NAPHTHENES BOILING AT ABOUT THE BOILING POINT OF NAPHTHALENE WITH A SELECTIVE SOLVENT FOR AROMATIC AND NAPHTHENE HYDROCARBONS, SEPARATING A RAFFINATE PHASE FROM AN EXTRACT PHASE CONTAINING SAID HYDROCARBONS AND RECOVEERING SAID HYDROCARBONS FROM SAID EXTRACT PHASE, (2) DISTILLATIVELY SEPARATING A "NAPHTHALENE FRACTION" BOILING WITHIN THE RANGE OF BETWEEN ABOUT 385* AND 455* F. FROM SAID EXTRACT HYDROCARBONS, (3) SUBJECTING SAID "NAPHTHALENE FRACTION" TO A CATALYTIC CRACKING OPERATION, AND (4) DISTILLATIVELY SEPARATING FROM THE LIQUID PRODUCT OF SAID CRACKING A NAPHTHALENE PRODUCT FRACTION. 